1. Field of the Invention
The present invention relates to an electron multiplier electrode and a terahertz radiation source using the electron multiplier electrode, and more particularly, to an electron multiplier electrode using a secondary electron extraction electrode and a terahertz radiation source using the electron multiplier electrode.
2. Description of the Related Art
A bandwidth of 1012 Hz has become important in application fields such as molecular optics, biophysics, medicine, spectroscopy, image processing and security. However, despite the importance of the bandwidth of 1012 Hz, terahertz radiation sources or multipliers have not yet been developed due to physical and engineering limits. Recently, terahertz radiation sources or multipliers have been actively developed and various methods have been attempted in order to develop terahertz radiation sources since various new relevant concepts and micromachining technologies have been developed.
FIG. 1 is a schematic view of such a conventional terahertz radiation source that has been developed. Referring to FIG. 1, the conventional terahertz radiation source includes: a substrate 1; an emitter 2 and an anode 6 that are disposed on the substrate 1 and face each other; and electron lenses 3, electron beam deflectors 4 and metal lattices 5 which are disposed between the emitter 2 and the anode 6. In this structure, while a path of an electron beam 8 is being adjusted by the electron lenses 3 and the electron beam deflectors 4, an electron beam 8 emitted from the emitter 2 proceeds towards the anode 6. During operation, the electron beam 8 passes by the metal lattices 5 which are disposed at regular intervals. At this time, terahertz electromagnetic waves 7 are generated due to the smith-purcell effect. The frequency of the electromagnetic waves 7 generated can be controlled by an interval between the metal lattices 5.
Meanwhile, as a structure for generating terahertz electromagnetic waves from an electron beam, photonic band gap crystals, cavity resonators and waveguide structures are known in addition to the above described smith-purcell radiation structure using the metal lattices 5.
However, in the case of the terahertz radiation source having the above described structure, since a current of the electron beam is very small when the size of the terahertz radiation source is small, it is not easy to radiate or amplify electromagnetic waves having a bandwidth of 1012 Hz. In terms of efficiency, an emission current emitted from an emitter should be very great and current density should be great as well, but in this state the lifetime of the emitter decreases.
Currently, technologies for solving this problem have been suggested using an electron multiplier microchannel plate. FIG. 2A is a view of a field emission circuit using an electron multiplier. Referring to FIG. 2A, the field emission circuit is configured in a structure in which an electron multiplier 14 is disposed between a cathode 11 and an anode 13, and an emitter 12, which is formed of a carbon nanotube (CNT), is disposed on the cathode 11. In this case, compared with a circuit of FIG. 2B in which the electron multiplier 14 is not disposed, it has been noted that the current of the electron beam reaching the anode 13 is about 7.5 times higher in the case of the circuit of FIG. 2A.
FIG. 3 is a schematic view of a conventional electron multiplier. Referring to FIG. 3, the conventional electron multiplier includes an insulating substrate 23 having a shape of a looped-type disk, upper and lower electrodes 24 and 25 that are respectively formed on upper and lower surfaces of the insulating substrate 23, a resistance layer 26 formed on an inner surface 23a of the insulating substrate 23, and a secondary electron extraction electrode 27 formed on the resistance layer 26. The secondary electron extraction electrode 27 may be formed of an oxide (e.g., MgO, SiO2 and La2O3) or a fluoride (CaF2 and MgF2) having a large secondary electron coefficient.
In such a structure, when a voltage is applied between the upper and lower electrodes 24 and 25, the electron beam incident in a hole 28 of the insulating substrate 23 collides with the secondary electron extraction electrode 27, and then the electron beam is accelerated and emitted from the hole 28 together with a secondary electron due to a potential difference between the upper and lower electrodes 24 and 25.
In the case of the electron multiplier having the above structure, in order to maximize extraction of the secondary electrons, a high voltage should be applied between the upper and lower electrodes 24 and 25. In this case, a current flows along the resistance layer 26 having a resistance of several MΩ. Accordingly, breakdown is likely to occur between the upper and lower electrodes 24 and 25 due to the high voltage. In addition, due to the current flowing along the resistance layer 26, a final electron extraction current can not be greater than the current of the resistance layer 26. Due to the current flowing along the resistance layer 26, heat problems or physical damage can also occur.